The modern industrial era has provided mankind with numerous of chemical substances improving life conditions and overall health situation. It is however also well-known and recognized that in the ever ending search for more cost effective substances and processes, the long term effect on environmental conditions arising from uncontrolled use of these substances and processes has for a long period of time been, and sometimes still are, neglected.
The use of halogenated hydrocarbons (for instance chlorinated compounds) in a variety of applications has created health and environmental problems as these substances often are very stable and tend to accumulate in living bodies.
In industrial sites or other places where the handling of such substances has been poor from environmental and health hazard aspects, halogenated hydrocarbons have been accumulated in the soil and ground water and can constitute a long term threat against health and environment. It is therefore of outmost importance to find methods and materials suitable for reducing the content of halogenated hydrocarbons in polluted soil, water and ground water. As these pollutants may be contained in large volumes of e.g. soils at various concentration levels, materials to be used for decomposing and reducing contents of pollutants should preferably be fairly inexpensive and have an ability to be effective at various concentration levels and varying overall conditions.
Remediation technologies are many and varied but can be categorized into ex-situ and in-situ methods. Ex-situ methods involve excavation of effected soils and subsequent treatment at the surface. In-situ methods seek to treat the contamination without removing the soils. The more traditional remediation approaches (used almost exclusively on contaminated sites from the 1970s to the 1990s) consists primarily of soil excavation and disposal to landfill (“dig and dump”) and groundwater (“pump and treat”). In situ technologies include solidification and stabilization and have been used extensively in the USA.
One interesting in-situ remediation technology for treating halogenated/chlorinated hydrocarbon contaminated soil, water or ground water is based on decomposition of the substances into less harmful species of which one end product being chloride-ions.
Iron in elemental form, so called zero-valent iron (ZVI), has been proposed by many inventors and scientists for decomposing halogenated hydrocarbons in soil and water. ZVI alone and in combination with various elements and substances have been described in this context as well as methods for the use thereof. As iron is a fairly inexpensive material, has high redox capability and low health and environmental impact, iron is a most suitable agent for this purpose.
Patent application WO2004/007379 describes support catalysts for in situ remediation of soil and/or groundwater contaminated with chlorinated hydrocarbons, comprising activated carbon as an absorbent and impregnated with ZVI. Examples of suitable shape of ZVI are powder, turnings or chips. Among others, the application also discloses support catalysts made by pyrolizing a mixture of activated carbon and iron salt followed by reducing the formed iron oxide to ZVI.
In U.S. Pat. No. 7,635,236 to Zhao, a method is disclosed for preparing highly stabilized and dispersible ZVI nanoparticles and using the nanoparticles in a remediation technology against inorganic chemical toxins in contaminated sites. The patented method comprises: providing a composition of ZVI nanoparticles dispersed in an aqueous carrier and stabilizer comprising carboxymethyl cellulose and delivering said composition to the contaminated site.
US patent application 2009/0191084 (Liskowitz) teaches ZVI in the form of particles or iron wool enriched with graphite carbon and sulphur which is supposed to create catalytic sites on the surface of the ZVI, promoting atomic hydrogen formation in a aqueous oxygen containing environment polluted with e.g. trichloroethylene. The formed atomic hydrogen will promote reduction of trichloroethylene to ethylene and ethane. Pure ZVI on the other hand tends to promote a reaction chain involving direct electron transfer from the corroding iron to the dissolved contaminating compound. In the case of trichloroethylene this compound will thus decompose into 1,2 cis-dichloroethylene and further into vinylchloride which is regarded as more harmful than the original compound. Atomized ZVI with a content of at least 4% graphite carbon and 0.5% sulphur is recommended.
US patent application 2010/0126944 discloses degradation of organic nitro compounds, especially nitro aromatic compounds and nitroamines, with bimetallic particles comprising ZVI having discontinuous coatings of metallic copper on the surface thereof. Higher rates of degradation are achieved when the water has a pH of 3.5-4.4 and especially when acetic acid is present in the water.
Patent application US 2011/0130575 describes a clay comprising a 2:1 aluminosilicate having negative charged sites; the 2:1 aluminosilicate clay containing sub-nano-sized ZVI particles distributed on the clay surface. Methods of synthesizing the novel clay is also described as well as its use in remediation applications e.g. dechlorination reductions.
Korean patent KR1076765B1 discloses nitrate reduction of water using ZVI combined with nickel, palladium or copper.
EP patent EP0506684 to Gilham discloses a procedure for cleaning a halogenated organic contaminant from groundwater in an aquifer by contacting the polluted ground water with a metal body, e.g. ZVI in the form of filings, particulates, fibers etc. under anaerobic conditions.
Many of the disclosed ZVI containing materials used for remediation of halogenated hydrocarbon polluted soil or waters include nano-sized ZVI particles of which the production is very costly while the function of others is based on a synergetic effect between ZVI and a costly metal. Thus there is a need for an efficient and cost effective ZVI based material for remediation, and especially for in-situ remediation, of halogenated hydrocarbon polluted soil, water or ground water.